Sorry for the vague title. I'm on the hunt for a different sutta this time!

From what I recall, the Buddha was speaking to someone about the urgency with which one should undertake the holy life. The other person would suggest things such as 'I will start practicing tomorrow morning', 'after this meal', 'after this mouthful of food', to all of which the Buddha replied as being heedless. The Buddha then stated that one who aspires to live long enough only to breathe in again after breathing out is truly following his teaching, or something along those lines..

It's not ringing a bell for me. Either I've forgotten the story (but it sounds memorable...), or it's in the Anguttara Nikaya, or otherwise.

"And how is it, bhikkhus, that by protecting oneself one protects others? By the pursuit, development, and cultivation of the four establishments of mindfulness. It is in such a way that by protecting oneself one protects others.

"And how is it, bhikkhus, that by protecting others one protects oneself? By patience, harmlessness, goodwill, and sympathy. It is in such a way that by protecting others one protects oneself.- Sedaka Sutta [SN 47.19]

AN 6.19 PTS: A iii 303 Maranassati Sutta: Mindfulness of Death (1) translated from the Pali by Thanissaro Bhikkhu

(Thanks be to Thanissaro Bhikkhu).

I have heard that at one time the Blessed One was staying at Nadika, in the Brick Hall. There he addressed the monks, "Monks!"

"Yes, lord," the monks replied.

The Blessed One said, "Mindfulness of death, when developed & pursued, is of great fruit & great benefit. It gains a footing in the Deathless, has the Deathless as its final end. Therefore you should develop mindfulness of death."

When this was said, a certain monk addressed the Blessed One, "I already develop mindfulness of death."

"And how do you develop mindfulness of death?"

"I think, 'O, that I might live for a day & night, that I might attend to the Blessed One's instructions. I would have accomplished a great deal.' This is how I develop mindfulness of death."

"I think, 'O, that I might live for a day, that I might attend to the Blessed One's instructions. I would have accomplished a great deal.' This is how I develop mindfulness of death."

Then another monk addressed the Blessed One, "I, too, develop mindfulness of death." ... "I think, 'O, that I might live for the interval that it takes to eat a meal, that I might attend to the Blessed One's instructions. I would have accomplished a great deal.' ..."

Then another monk addressed the Blessed One, "I, too, develop mindfulness of death." ... "I think, 'O, that I might live for the interval that it takes to swallow having chewed up four morsels of food, that I might attend to the Blessed One's instructions. I would have accomplished a great deal.' ..."

Then another monk addressed the Blessed One, "I, too, develop mindfulness of death." ... "I think, 'O, that I might live for the interval that it takes to swallow having chewed up one morsel of food, that I might attend to the Blessed One's instructions. I would have accomplished a great deal.' ..."

Then another monk addressed the Blessed One, "I, too, develop mindfulness of death." ... "I think, 'O, that I might live for the interval that it takes to breathe out after breathing in, or to breathe in after breathing out, that I might attend to the Blessed One's instructions. I would have accomplished a great deal.' This is how I develop mindfulness of death."

When this was said, the Blessed One addressed the monks. "Whoever develops mindfulness of death, thinking, 'O, that I might live for a day & night... for a day... for the interval that it takes to eat a meal... for the interval that it takes to swallow having chewed up four morsels of food, that I might attend to the Blessed One's instructions. I would have accomplished a great deal' — they are said to dwell heedlessly. They develop mindfulness of death slowly for the sake of ending the effluents.

"But whoever develops mindfulness of death, thinking, 'O, that I might live for the interval that it takes to swallow having chewed up one morsel of food... for the interval that it takes to breathe out after breathing in, or to breathe in after breathing out, that I might attend to the Blessed One's instructions. I would have accomplished a great deal' — they are said to dwell heedfully. They develop mindfulness of death acutely for the sake of ending the effluents.

"Therefore you should train yourselves: 'We will dwell heedfully. We will develop mindfulness of death acutely for the sake of ending the effluents.' That is how you should train yourselves."

That is what the Blessed One said. Gratified, the monks delighted in the Blessed One's words.